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Abell 2744 (Pandora's Cluster)


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Abell 2744
Pandora's Cluster (パンドラ銀河団)
Cluster of Galaxies (銀河団)



星座 (Constellation)

ちょうこくしつ座 (Scl) (Sculptor)



距離 (Distance)

35億光年 (3.5 billion light-years)

Abell 2744 (Pandora's Cluster) is a cluster of galaxies located 3.5 billion light years from the Earth in the constellation Sculptor.

Abell 2744 (Pandora's Cluster) : Picture

Abell 2744 (Pandora's Cluster)
Abell 2744 (Pandora's Cluster)
(C) NASA/ESA/STScI
This long-exposure image from NASA's Hubble Space Telescope of massive galaxy cluster Abell 2744 is the deepest ever made of any cluster of galaxies. It shows some of the faintest and youngest galaxies ever detected in space. Abell 2744, located in the constellation Sculptor, appears in the foreground of this image. It contains several hundred galaxies as they looked 3.5 billion years ago. The immense gravity in Abell 2744 acts as a gravitational lens to warp space and brighten and magnify images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did longer than 12 billion years ago, not long after the big bang.

This image is part of an unprecedented long-distance view of the universe from an ambitious collaborative project among NASA's Hubble, Spitzer and Chandra space telescopes called The Frontier Fields. Over the next several years, select patches of the sky will be photographed for the purpose of better understanding galaxy evolution. This visible-light and near-infrared composite image was taken with Hubble's Wide Field Camera 3.

Pandora's Cluster
Pandora's Cluster Revealed
(C) X-ray: NASA/CXC/ITA/INAF/J. Merten et al. Lensing: NASA/STScI; NAOJ/Subaru; ESO/VLT Optical: NASA/STScI/R. Dupke
One of the most complicated and dramatic collisions between galaxy clusters ever seen is captured in this new composite image. This collision site, known officially as Abell 2744, has been dubbed "Pandora's Cluster" because of the wide variety of different structures seen. Data from NASA's Chandra X-ray Observatory are colored red, showing gas with temperatures of millions of degrees. In blue is a map showing the total mass concentration (mostly dark matter) based on data from the Hubble Space Telescope (HST), the European Southern Observatory's Very Large Telescope (VLT), and the Japanese Subaru telescope. Optical data from HST and VLT also show the constituent galaxies of the clusters.

The "core" region shows a bullet-shaped structure in the X-ray emitting hot gas and a separation between the hot gas and the dark matter. (As a guide, local peaks in the distribution of hot gas and overall matter in the different regions are shown with red and blue circles respectively). This separation occurs because electric forces between colliding particles in the clouds of hot gas create a friction that slows them down, while dark matter is unaffected by such forces.

In the Northwest ("NW") region, a much larger separation is seen between the hot gas and the dark matter. Surprisingly, the hot gas leads the "dark" clump (mostly dark matter) by about 500,000 light years. This unusual configuration may require a slingshot scenario, as suggested previously by scientists, to fling the hot gas ahead of the dark matter during an earlier interaction. In the North ("N") and the West ("W") two additional examples of hot gas separated from dark matter may be visible. The latter appears to exhibit the largest separation seen to date between hot gas and dark matter.

The authors of this study retraced the details of the collision, and deduce that at least four different galaxy clusters coming from a variety of directions were involved. To understand this history, it was crucial to map the positions of all three types of matter in Abell 2744. Although the galaxies are bright, they make up less than 5% of the mass in Abell 2744. The rest is hot gas (around 20%) visible only in X-rays, and dark matter (around 75%), which is completely invisible.

Dark matter is particularly elusive as it does not emit, absorb or reflect light, but only makes itself apparent through its gravitational attraction. To pinpoint the location of this mysterious substance the team used a phenomenon known as gravitational lensing. This is the bending of light rays from distant galaxies as they pass through the gravitational field present in the cluster. The result is a series of telltale distortions in the images of galaxies in the background of optical observations. By carefully plotting the way that these images are distorted, a map is constructed of where the mass - and hence the dark matter - actually lies (shown in blue).

Galaxy clusters are the largest gravitationally bound objects in the Universe and have become powerful tools in cosmology studies. Further studies of Abell 2744 may provide a deeper understanding of the way that these important objects grow and provide new insight into the properties of dark matter.

Abell 2744 (Pandora's Cluster) Abell 2744 (Pandora's Cluster)
Abell 2744 (Pandora's Cluster)
(C) NASA
Abell 2744 (Pandora's Cluster)
(C) NASA
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Abell 2744 (Pandora's Cluster) : Movie

Hubblecast 47: Pandora's Cluster
This joint episode of the Hubblecast and ESOcast presents Abell 2744, an unusual cluster of galaxies nicknamed "Pandora's Cluster" by the astronomers who have studied it. Looking at the galaxies, gas and dark matter in the cluster, scientists have reconstructed the series of huge collisions that created it, and have uncovered some strange phenomena never seen together before.
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